Mixotrophic Culture Of High Selenium-enrich Spirulina Platensis And The Speciation Of Selenium

The trace mineral selenium (Se) is an essential nutrient of fundamental importance to human biology. Spirulina platensis (S. platensis ) was found to possess a good tolerance to high levels of Se, indicating that it was a good carrier for Se biotransformation. The effects of different Se adding methods on S. platensis were investigated. The speciation of Se existing in the microalgae cells and volatile Se metabolized to the environment, the morphological changes of S. platensis cultured under autotrophic, heterotrophic and mixotrophic conditions were also carried out in this study. Some meaningful results were obtained.1. Se has either stimulating or toxic effects on the culture of S. platensis depending on the Se levels in media. S. platensis could bioaccumulate Se efficiently during the cultivation time and the accumulation amount increased with Se stress (≤ 150 mg/L). The higher initial Se concentrations (≥200 mg/L) led to high Se enrichment, but inducing much lower biomass concentrations and some active substances. The results revealed that the majority of the total Se was accumulated in a short time (about 3 days) and most of them were biotransformed into organic Se (about 90 %) by integrating with the algal bioligands, such as proteins, lipids, polysaccharides and other algal components.2. Effects of different Se adding methods on the growth, Se accumulation and transformation of S. platensis were investigated. The results indicated that the high Se-enriched S. platensis with a total Se content of 1301.17 μg/g and an organic ratio of 86.85 % can be obtained while the Se was added in the 7th, 8th, 9th day respectively with an accumulative concentration of 1000 mg/L. A stimulative effect in biomass of Se-enriched cultures was observed in the 7 th experimental set, comparing with the control. Furthermore, the contents of phycobiliproteins, and photosynthetic pigments (Lutein and β -carotene) increased to some extend. About 67.12% of the organic Se existed in the part of soluble proteins.3. A reversed phase high performance liquid chromatographic (RP-HPLC)method with precolumn derivazation of dansyl (Dns-Cl), and a Waters AccQ-Tag method for simultaneous determination of 18 common amino acids and selenomethionine (Se-Met) was established.4. The amino acids in Se-enriched S. platensis were analyzed with the Dns-Cl HPLC method. The peaks area of the 19 amino acids linearly correlated with their concentrations. Detection limit was 3.5×10^-8 mol/L. The quantitative analysis showed that Se-enriched treatment didn't change the content of 18 common amino acids in Se-SP. The content of Se-Met was 0.261 mg/g in the Se-SP. The detection linearity, precision and recovery associated with this assay were evaluated.5. Methylation is an effective detoxification mechanism. A new method was developed for the fast determination of trace amounts of volatile Se in culture media of S. platensis. The results indicated that the chief methylation productions of Se biotransformation by S. platensis were dimethylselenide (DmSe) and dimethyldiselenide (DMDSe).6. The morphological changes of S. platensis cultured under autotrophic, heterotrophic and mixotrophic conditions were also studied. The difference among the ultrastructure of S. platensis cells may be due to the photosynthesis and rapid intake of organic carbon resource.